Radio telephone monitoring system



Sept. 2l, 1937.

H. M. PRUDEN RADIO TELEPHONE MONITORING SYSTEM Filed May 19, 1956 3 Sheets-Sheet 1 @wk in.

/N VENTO/Q HM PRUDE N By A T TORNE Y Sept.`2l, 1937. H. M. PRUDEN RADIO TELEPHONE MONITORING SYSTEM Filed May 19, 1936 5 Sheets-Sheet 2 /A/ VEA/TOR H. M. PRUDE N NR.. l u,

NGN n A TTOR/VE V Sept. 21, 1937. H. M. PRUDEN 2,093,847

RADIO TELEPHONE MONITORING SYSTEM Filed May 19, 1956 .TMSheets-Sheet 3 H/GH FREQ.

AMP. AND

IS7' DET CHANNEL 6 X /Nl/ENTOR By HM. PRI/DEN A TTG-RNE V Patented sept. 21, 1937 f 2,093,847l

STATES PATENT OFFICE RADIO TELEPHONE MONITORING SYSTEM Harold M. Pruden, Maplewood, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 19, 1936, Serial No. 80,529

12 Claims. (Cl. Z50-20) This invention relates to radio telephone cirfrequencies of 600, 1050, 1500 and 1950 cycles, recuits and more particularly to facilities for enspectively.

abling monitoring to be accomplished on a plu- In accordance with one embodiment of the inrality of radio telephonereceiving channels vention three intermediate frequency receiving 5 which are used on a shared time basis. channels are provided two of which are used for 5 In some instances it is ldesirable to use one service connections and the third for monitoring receiver for monitoring on any one of a pluralpurposes. Three groups of switching relays are ity of receiving channels each served by a diierprovided for connecting any one of a plurality ent directive receiving antenna. One of these of high frequency receiving channels to any one channels may be arranged, for example, to reof the three intermediate frequency channels. 10 celve on one frequency band from two or more The output of the intermediate frequency monitransm-itting stations, a second channel may be toring channel is connected through a transarranged to receive on another frequency band former to a plurality of signaling frequency from two or more transmitting stations, a third filters each arranged to pass a different signall5 channel may be arranged to receive on another ing tone frequency and also through an untuned 15 frequency band from two or more transmitting transformer to a diode tube. The output of each stations and other channels to receive on other lter is connected to a detector tube in the plate frequency bands from one or more transmitting circuit of which a relay is connected. The elecstations. Where the directivity of the antennae trodes of the diode tube are connected to the grid 2O is sufficiently defined and the stations transmitbiasing circuit of the several detector tubes. 20 ting are operating on different frequencies, no When the monitoring channel is connected to great difficulty is encountered in determining any high frequency receiving channel, the tone which station is being received. However, where Signal SuDeImpOSed 011 the Carrier fOr identifyreception is required over several antennae, as ing ASi particular transmitting Station Will be in the case assumed, from several transmitting passed by the signaling frequency filter which 25 stations operating on the same frequency band, is tuned to respond thereto thereby operating the antennae may not be sufficiently directive the relay of the detector tube associated with to determine definitely which of such stations that lter and thereby identifying the particular is transmitting. It is therefore the object of transmitting station. Should there be a noise or the present invention to provide a monitoring static disturbance on the high frequencychan- 30 system for enabling an accurate determination nel, the diode tube will function to increase the of the source of incoming radio reception. negative bias on` the grids of the detector tubes The manner in which this object may be atto desensitize them so that they will not respond. tained is disclosed herein. It is to be understood, A normally Operating Stp-byrstep selector however, that the disclosure is only illustrative switch is provided for successively operating the of two `embodiments of the invention and that relays of the group which connects the high freother equivalent circuits and apparatus might quency channels to the intermediate frequency be employed without departing from the scope monitoring channel, whereby the high frequency of the invention as defined in the appended channels may benmonitored on in rotation for claims. l identifying to the monitor the particular high 40 In accordance with the present invention profrequency channel which is connected at any vision is made for monitoring by a single retime for monitoring and for identifying the parceiver on any one of a plurality of receiving ticular transmitting station, reception from channels, each associated with a receiving anwhich is being received over that channel. A tenna. Each receiving channel comprises high plurality of signal lamps is provided which are 45 frequency amplifier and first detector panels selectively controlled by the plate relays of the tuned to receive on a particular high frequency signaling frequency detector tubes over wipers of carrier band from one or more transmitting the selector switch. stations. The carrier band transmitted from dif- Keys are also provided for enabling the moni- CJD ferent stations may be modulated by tone sigtor to cause the selector switch to automatically 50 nals of relatively low frequency by means of pass by any high frequency channel upon which which each transmitting station may be distincmonitoring at the time is not desired. A bank of tively identified. Thus, for example, four stakeys is also associated with each intermediate tions transmitting on the same carrier frequency frequency service channel by means of which the l band could be identified by four modulating tone monitor may operate the relays for associating any high frequency channel on which incoming signals have been detected by the monitoring channel, as indicated by a lighted signal lamp, with an intermediate frequency channel for a service connection.

In some instances individual station identication may not be required and therefore the tuned filters, detectors and signaling equipment may be eliminated and a monitoring loud-speaker used in lieu thereof as disclosed in a second embodiment of the invention. In this embodiment of the invention, the same provision is made for connecting the high frequency channels in rotation to an intermediate frequency monitoring channel and for connecting any high frequency channel to an intermediate frequency service channel for service connections. Signal lamps are provided for indicating to the monitor which cf the high frequency channels is being monitored on at any instant. The output of the intermediate frequency monitoring channel is connected to a loud-speaker by means of which the monitor may determine when an incoming call is being received on any high frequency channel which is at the time connected for monitoring. A bank of keys is provided, one for each high frequency channel for enabling the monitor to switch any highV frequency channel upon which an incoming call has been detected to one or the other intermediate frequency service channel and to thereby cause the selector switch to pass by such channel during its rotation. A second bank of keys is also provided, one for each high frequency channel for enabling the monitor to hold the high frequency channel connected to the monitoring channel or to cause the selector switch to pass by such channel during its rotation.

It is believed that a clearer understanding of the invention and its mode of operation may be obtained from a consideration of the following detailed description taken in connection with the accompanying drawings of which:

Fig. l 'discloses one embodiment of the invention arranged for successively monitoring on any one of a plurality of high frequency receiving channels and for the automatic detection and identification of any one of a plurality of transmitting stations receptionl from which may be received over the receiving channel being monitored on Figs. 2 and 3 taken together with Fig. 3 placed beneath Fig. il show a second embodiment of the invention from which the apparatus for the automatic detection and identification of transmitting stations has been omitted, Fig. l showing the high frequency receiving channels, the intermediate frequency receiving channels and certain switching equipment and Fig. 2 showing a further high frequency receiving channel, the switching equipment associated therewith, and a selector switch whereby the high frequency receiving channels are switched in rotation to the intermediate frequency monitoring channel.

Referring rst to the embodiment of the invention disclosed in Fig. l, it will be assumed that monitoring on three high frequency receiving channels is required and that reception from any one of four transmitting stations may be incoming on any one of these receiving channels. The high frequency receiving channels are schematically illustrated by the boxes I, 2 and 3 and each comprises a receiving antenna system, a high frequency amplifier panel and a first detector panel. Three'intermediate frequency receiving channels are provided as indicated by the boxes 4, 5 and 6, each comprising an intermedin ate frequency amplifier, second detector, an audio frequency amplifier and power unit. Two of these intermediate frequency channels 4 and 5 are connected on their output sides to service channels and the third channel 6 is connected on its output side to a tone signal detection circuit.

A group of switching relays i, S and 9 is p-rovided for connecting the input circuits of intermediate frequency channel I with the output circuit of any one of the high frequency receiving channels I, 2 or 3. A second group of switching relays Ill, II and I2, is provided for connecting the input circuit of intermediate frequency channel 5 With the output circuit of channel l, 2 or 3 and a third group of switching relays I3, Ill and I5 is provided for connecting the input circuit of intermediate frequency monitoring channel 0 withthe output circuit of channel I, 2 or 3. The operation of relays 'f to I2, inclusive, are controlled by keys I6 to 2l, inclusive, individual respectively. thereto and relays I3, I4 and I5 are operated in rotation under the control of the step-bystep selector switch 50 in a manner to be hereinafter described.

The output of the audio frequency amplifier of the intermediate frequency monitoring channel 6 is connected over the back contacts of relay 22 in parallel to the primary windings of transformers 23 and 2G. The secondarywinding of transformer 23 is connected in parallel to the primary windings of four transformers 25A, 25B, 25C and 25D which are respectively tuned by filter circuits 25A, 25B, 26C and 26D. If it be assumed that four signaling frequencies of 1950, 1500 1050 and 600 cycles are employed for station identification, these filters would be designed to tune the transformers to these frequencies; filter 25C tuning transformer 25C to frequency C of 1950 cycles, filter 26A tuning transformer 25A to frequency A of 1500 cycles, filter 25Dl tuning transformer 25D to frequency D of 1050 cycles, and filter 26B tuning transformer 25B to frequency B of 600 cycles.

The secondaries of transformers 25C, 25A, 25D and 25B are connected respectively to the grids of detector tubes TC, TA, TD and TB, negative biasing potential being applied therethrough to the grids of these tubes from the battery 2l', through resistance 28. The plate of each detector tube is connected through the winding of a plate relay to the positive terminal of plate battery 29, the plate of tube TC being connected through the winding of relay PC, the plate of tube TA being connected through the winding of relay PA, the plate of tube TD being connected through the winding of relay PD and the plate of tube TB being connected through the winding of relay PB. Each of the plate relays upon operating controls the operation of a secondary relay, relay PD for example controlling the operation of relay RD over an obvious circuit.

Although units comprising lter tuned transformers, detector tubes and relays controlled thereby have been disclosed for selective response to four different signaling frequencies, it is to be understood that additional units may be supplied if more than four stations are arrangedto transmit on the same carrier frequency to be recevied over the same high frequency receiving channel.

The secondary of untuned transformer 24 is connected across the elements of the diode tube 3l) and its output is adjusted to be approximately twenty decibels less than that of any of the tuned transformers. The output of the diode tube 30 is used to control the grid bias of all of the detector tubes TC, TA, TD and TB since if the noise or static level is high the effect of the diode tube will be to produce a direct current voltage drop across resistance 2S and thereby raise the negative bias on the grids of the tubes and thus serve as a noise desensitizer. The system is thus Capable of operating through extraordinary noise conditions and is practically free from false operation on either voice or noise currents.

For connecting the high frequency receiving channels in rotation to the monitoring channel 6 and for placing channel signal lamps successively under the control of the signal detection circuit, a rotary step-by-step selector switch 53 is provided. This switch is actuated step-bystep by its stepping magnet I under the control of interrupter 3i to advance its wipers over their respective arcuate banks of terminals. Under the assumption that the system is designed to function in response to four oliiferent signaling frequencies four wipers 52 to 55, inclusive, are provided which are connected with contacts of relays RA, RB, RC and RD responsive respectively to the four signaling frequencies A, B, C and D. The three equipped terminals of the arc associated with wiper 54 are connected to the windings of relays IA, 2A and 3A which control the circuits of signal lamps ILA, 2LA and 3LA. The equipped terminals of the are associated with wiper 52 are connected to the windings of relays IB, 2B and 3B which control the circuits of lamps ILB, 2LB and SLB. The equipped terminals of the arc associated with wiper 55 are connected to the windings of relays IC, 2C and 3C which control the circuits of lamps ILC, 2LC and SLC and the equipped terminals of the arc associated with wiper 53 are connected to the windings of relays ID, 2D and 3D which control the circuits of lamps ILD, 2LD and SLD.

In the designation of these relays and lamps, the preX numeral indicates the high frequency receiving channel to which they are allocated and the suffix letter indicates the signaling frequency and thus a particular transmitting station, reception from which may be received over that channel. Thus the relays IA, IB, IC and ID and the lamps ILA, ILB, ILC and ILD form One group allocated to the No. I receiving channel for identifying respectively four stations employing the modulating signaling frequencies A, B, C and D. Should it be found necessary to identify more channels, other groups of relays and lamps would be added, the relays being controlled over other terminals of the arcs of switch 50. Also should it be found necessary to identify more than four stations on any channel, additional detector units each comprising a lter tuned to another signaling frequency, detector tube and relays such as PA and RA would be provided as previously stated and an additional wiper would be added to the switch 53 for each such unit and other relays and lamps such as IA and ILA would be added to each group of relays and lamps in the indicator.

Under the assumption that monitoring is required on but three high frequency receiving channels, three terminals of the arc with which wiper 56 cooperates are connected over back contacts of the skip channel relays 32, 33 and 34 to the windings of switching relays I3, Ill and I5 so that as the switch 55 advances, these switching frequency service channel 4l or 5.

relays are operated in rotation to successively connect the three high frequency channels I, 2 and 3 with the monitoring channel 8. The remaining terminals of this switch arc are strapped together to cause the switch to pass over them quickly. Should other high frequency receiving channels be added, the switching relays thereof corresponding to relay I3 would be controlled over terminals of the arc associated with wiper 56.

Keys 35, 36 and 3'! are provided for operating the skip channel relays 32, 33 and 34 when for any reason it becomes desirable to omit monitoring on any high frequency channel for causing the selector switch 5G to pass by that channel without causing its connection to the monitoring channel 5.

Having now described the apparatus disclosed in Fig. 1, the mode of its operation will now be discussed. It will be assumed that the selector switch 53 is standing in the position disclosed and that therefore the circuit of switching relay I S is established from battery, winding of relay I3, back Contact of relay 32, the terminal on which wiper 55 is temporarily standing to ground. Relay I3 therefore operates and connects the output circuit of high frequency receiving channel I to the input circuit of the monitoring channel 6. It will now be assumed that reception is received in the monitoring channel from a transmitting station which is identified by the modulating signaling frequency A and that therefore the output of the monitoring channel 5 is applied over the back contacts of relay 22 through the transformer 23 and is passed by transformer 25A, tuned by lter 25A to the input of detector tube TA. The detector tube TA will therefore respond, operating its plate relay PA and in turn relay RA. Since this particular signaling frequency A cannot pass the tuned filters 26B, 26C and 26D no other tube will respond and the relays controlled thereby will not operate. With relay RA operated, a circuit is closed from ground over its contacts wiper 5d and the terminal with which it is engaged, winding of relay IA to battery over the normally closed contacts of release key 38. Relay IA now operates locking in a circuit frorn battery over the contacts of key 33, winding and right front contact of relay IA, conductor 33, normal conta-cts of keys I9 and I5, to ground and closing a circuit for lamp ILA, extending from battery over the contacts of key 38, left front contact of relay IA, lamp ILA to ground or if desired to ground through an auxiliary signaling device not shown. The lighting of lamp ILA indicates to the monitor that the reception from a station identified by signaling frequency A is being received over the receiving channel I. The monitor may now connect the high frequency channel I to a free intermediate If channel fl is free, he will. operate key I6 thereby operating switching relay i to connect the channel I to channel li. The operation of key I6 also opens the locking circuit of relay IA which will then release and extinguish lamp ILA as soon as the switch 5i! advances another step, and closes an obvious circuit through the lower winding of skip channel relay 32 to prevent monitoring on channel I as long as it is connected for a service connection.

When the interrupter 3l next closes its contact:` a circuit is established from ground thereover, normally closed contacts of stopI key iii,

winding of stepping magnet 5I to battery, whereby the wipers of switch 50 are advanced one step,

and a circuit is closed in parallel therewith through the winding of relay 22. Relay 22 upon operating opens the output circuit of the monitoring channel during the time that the switch is advancing to its next monitoring position. When wiper 54 leaves the terminal on which it was resting, relay IA releases if either key i or I9 has been operated and causes lamp lLA to become extinguished.

It will now be assumed that a station identined by the signaling frequency C is transmitting and reception therefrom is being received over high frequency channel 2. A circuit is now established from ground over wiper 5% and the terminal with which it is now engaged, back contact of relay 33, winding of switching relay iii, thereby connecting channel 2 with the monitoring channel 3. Relay 22 having now released, the output of channel 6 is connected through transformer 23 to the tuned transformers 25A, 25B, 25C and 25D and since the signaling reception incoming over channels 2 and E is modulated with frequency C, the tuned transformer 25C passes this frequency causing the detector tube TC to function, and operate relays PC and RC. With relay RC operated a circuit is established over its contacts, wiper 55 and the terminal with which it is engaged, winding of relay 2C to battery over the contacts of key 38.

Relay 2C operates locking over its right front contact, conductor i2, normal contacts of keys E@ and I1 to ground and closing the circuit of lamp 2LC. The lighting of lamp 2LC apprises the monitor that reception from a station identified by the signaling frequency C is being received over channel 2. The monitor may now complete a service connection from channel 2 to intermediate frequency service channel for example, by operating switching relay il through ie operation of key 29. The operation of key 2i] also establishes an obvious circuit through the lower winding of skip relay 33 which operates to prevent monitoring on channel 2 so long as it is connected for a service connection and opens the locking circuit of relay 2C.

'When the interrupter 3i again closes its contacts, relay 22 is again operated and switch 5G advances its wipers another step. in its aclvanced position, switching relay i5 is operated over wiper 3S to connect channel 3 to the monitoring channel 6 and the rela-ys 3A, 3B, 3C and 3D are connected over wipers 53, 52, 55 and 53, respectively, to the contacts of relays RA, RB, RC and RD preparatory to registering the identiication of any station, reception from which may be incoming over channel 3.

On the next closure of the contacts of interrupter SI, the switch 5I) is advanced another step whereupon a self-interrupting circuit is established from ground over wiper 56 strapped terminals of the arc with which it is associated, interrupter contacts and winding of stepping magnet 5i to battery whereby the switch is quickly advanced into the position in which the first channel I is again monitored. if the previously established service connection from channel i over channel 4 is still effective, relay 32 will be operated and the switch 56 will at once be quickly advanced one step by a circuit established from ground over wiper 5S, front contact of'relay 32, interrupter contacts and winding of stepping magnet 5I to battery and no circuit for switching relay I3 will be established. In a similar manner if the service connection from channel I over channel 5 is still effective, relay 33 will be operated and switch 5I! will be advanced immediately into a position for` monitoring on channel 3 without establishing any monitoring connection from channel 2 to the monitoring channel.

Monitoring on any high frequency channel may be skipped at the option of the monitor by operating one of the keys 35, 36 or 31 individual to these channels. For example, the operation of key 31 causes the operation of relay 34 which is effective to open the operating circuit of switching relay I5 thus preventing the connection of channel 3 to the monitoring chann-el 6 and prepares a circuit for causing switch 50 to quickly pass by this channel when it is advanced to the position in which this channel would normally be monitored. Should the monitor desire to stop the switch at any time, he may do so by operating the key l. The key 38 when operated will restore any operated indicator relay and extinguish the lamp whose circuit is controlled thereby.

Consideration will now be given to the further embodiment of the invention disclosed in Figs. 2 and 3 which is similar to that disclosed in Fig. 1 except that the specific identification of the particular station transmitting is not made but only an identification of each high frequency channel as it is being monitored upon. In these figures, it is assumed that six high frequency receiving channels Ztl, 222, 2Ei3--26 are equipped, provision being possible for the further expansion of the system to monitor on four additional channels. Shouid an ultimate of twenty-two channels be required, the step-by-step selector switch 25D could be replaced by a larger switch having twenty-two terminals in its arc rather than ten as disclosed.

Three intermediate frequency channels 201, 298 and 209 are provided each comprising an intermediate frequency amplifier, second cletector, audio frequency amplifier and power unit as indicated by the boxes. Two of these channels 2t? and 2% are connected on their output sides to service channels and the third or monitoring channel '26S is connected on its output side to a monitoring device such as the loud-speaker Zi.

Associated with each high frequency channel are three switching relays and two three-position The switching relays associated with each channel are effective when operated to connect the output circuit of the particular channel with the input circuit of any one of the three intermediate frequency channels 291, 263 or 209. For example, relay 2l i when operated connects channel ZI to service channel 281; relay 22| when operated connects channel 2EJI to service channel 203; and relay 23| when operated connects channel 20| to the monitoring channel 239. Similarly relay .2!2 is effective to connect channel 262 to service channel 251, relay 222 is effective to connect channel 292 to service channel 23 and relay 232 is effective to connect channel 202 to monitoring channel 29.

One key associated with each channel controls the operation of two of the switching relays to connect the channel with either one of the two service channels and to connect the screen grid and plate conductors of the high frequency channel to the power unit of the service channel to which it becomes connected. The second key associated with each channel controls the operation of the third switching relay to connect the channel with the monitoring channel and to provide for the skipping of the channel in the manner to be later described. For example, key 24I when operated toits lower position establishes thel operating circuit of switching relay 2I| and connects the screen grid conductor S and plate conductor P for channel to the screen grid and plate supply leads S and P extending from the power unit of the service channel 291. When key 22| is operated to its upper position, it establishes the operating circuit of switching relay 22| and connects the screen grid and plate conductors S and P of channel 29| to the screen grid and plate supply conductors S and P extending from the power unit of service channel 299. When key is operated to its upper position, it establishes the operating circuit of switching relay 23| and closes a circuit for relay 258 to arrest the operation of selector switch 259 and when operated to its lower position establishes a circuit to cause the selector switch 259 to pass by channel 29| in its routine operation as will be later described. The keys associated with the other high frequency channels perform similar functions as will be obvious from an inspection of the drawings.

'Ihe selector switch 25|), having a stepping magnet 251, is provided for operating the switching relays 23|, 232, 233--236 in rotation to successively connectl the high frequency channels 29|, 292, 293-296 to the monitoring channel 299. The lamps 26|, 262, 263-266 .are also lighted in succession by the step-by-step advance of the selector switch to indicate to the monitor which channel is at any instant connected to the monitoring channel.

Direct current for operating the switching relays, lamps, selector switch and selector switch control relays 258 and 259 is supplied to the negative bus-bar 2|1 by the full-wave rectier 21B, for example of the copper oxide type, which is fed from the alternating current commercial power lines 2|9 and 226 through the control key 221 and the transformer 218. To insure that the selector switch 256 will step quickly from position to position and pause for a predetermined interval in each position, the polarized stepping relay 259 is provided, the operation of which is controlled by the charging and discharging of condenser 228.. The charging'and discharging of condenser 228 is controlled by the full-wave rectier 229 which may also be of the copper oxide type and which is fed from the power lines 2|9 and 229 through the transformer 236 under the control of the self-interrupting heat coil relay 231.

To guard against the transfer of extraneous operating frequencies, generated in the operating circuit, to the high frequency channels, filters such as 233 to 299, 241 to 2119, etc. each comprising a series inductance and two grounded condensers are provided. The lter 239 is connected between the negative bus-bar 2|1 and one terminal of each of the switching relays and the other filters are connected between the other terminals of the switching relays and the positive bus-bar or ground.

Having now described the apparatus of the monitoring system disclosed in Figs. 2 and 3, the manner in which it functions will now be discussed. To start the operation of the circuit, the key 221 is operated thereby applying power from the supply mains 219 and 229 through the stepdown transformer 213 to the input junctions of the rectier 2|8 and to the primary winding of transformer 23D. The alternating current applied to rectier 218 is rectified thereby to apply negative 24-volt direct current potential over one of its output junctions to bus-bar 2|1 and to apply positive potential to its other grounded output junction. This direct current will thereupon ow from the positive junction of the rectier through high resistance 269 and the winding of polarized relay 259 to the negative junction but relay 259 will not operate to close its front contact since it is biased by this current against its back Contact. With the heat coil relay 231 unenergized and the bi-metallic contact element controlled thereby cold' and engaging its back contact, the application of alternating current to the primary winding of step-down transformer 23|), induces current in the secondary winding thereof which is bridged across the input junctions of rectier 229 over the left back contact of relay 258 and the back contact of heat coil relay 231. The winding of heat coil relay 231, also bridged across the input terminals, become energized to heat its bi-metallic contact element and a direct current potential of approximately lll-volts is produced across the output terminals of the rectifier 229.

With 14-volts negative potential applied from rectifier 229 through resistance 261, to one side of condenser 228 and negative potential of 24'- volts applied through the winding of relay 259 to the other terminal condenser 228, the condenser charges through the winding of relay 259 and since the charging current now owing through the winding of polarized relay 259 will overcome the. biasing current supplied to the winding of this relay from the rectier 2|8, relay 259 will thereupon immediately operate its armature to its front contact to close the operating circuit of stepping magnet 251. This circuit may be traced from bus-bar 2|1 through the winding of magnet 251 to ground at the front contact of relay 259. After an interval determined by the capacitance of condenser 228 and the value of resistance 261 condenser 228 will become fully charged and charging current will cease to iiow through the winding of relay 259. The biasing circuit of relay 259 will thereupon become effective to operate the relay to open the circuit of magnet 251. Magnet 251 thereupon quickly advances wiper 268 of switch 256 one step.

When the winding of heat coil relay 231 has been energized for an interval, and its bi-metallic element has become suiciently heated it will `open its normally closed contact thereby disrupting the input circuit of the rectifier 229. With no potential across its output terminals the. charge on condenser 223 now leaks oi through resistance 261 and through the rectifier 229 to ground. The circuit through the winding of heat coil relay 231 being opened, its bi-metallic now cools and after an interval recloses the input circuit of rectifier 229. This cycle of operations will now be repeated so long as switch 221 is maintained closed causing switch 259 to step its wiper 268 quickly from terminal to terminal with a pause on each terminal determined by the operating time of the heat coil relay 231 and the charging time of condenser 228.

It will be assumed that at the time switch 221 was closed, the wiper 268 was standing on the No. terminal of its arc. With all of the channel keys in their normal positions a circuit is now established from the negative bus-bar 2|1 through filter 238, winding of switching relay 23|, filter 239 and in parallel therewith through signal lamp 26| over the left normal contacts of key 211| to the left normal contacts of key 25|,

-f I I conductor IBBA over vwhich1 the. receiving 1 channel f '11201:wasblecked against 'operation rby Ablocking I I l bias supplied yfron-1I thepcwer; unitof' the moni- I 1 conductor 211|,` terminal and .wiper 12581 ofy switch 1 I f 1 2150 'toground at the right' back Contact of :relayl 1 n 258. .Relay 23I operates and lamp 26 I lights. I l I 1 Relay123| upon operating opens its upper hack I 1 I contactsr thereby removing ground 1from lits upper 1 active contacts which ground 'normallyshieldsi the f 1 I relay contacts: against the; leakagel of high fre-I I I 1 'quency' energy vacross them; establishes lover its. 1 I upper -frcnt contacts the continuity of the inter-y f mediatefrequency/conductor IF, between the out-1 I I putoi'high frequency channel 20| and the input f of the intermediate frequency monitoringchannel I 209, :establishes over its lower front. contact' and the lowerl back contacts .of switching relays 2I1I 1 1 1 i and 22|, the. continuity of thebiasing .conductor B between `the output 1 o'iI channel. 20| and the. i I inputofmonitcringchannel 209, and at its lower 1 i *back 'contactfintercepts the :connection between' Ai I the hiasing conductor and ythe blocking-1 bias toringchannel 209. 1. .1 1 I With the blocking bias removed and'screen grid I f 1 I and plate potentials supplied over supplyconducl I l I tors S Iand 'P .and the :right normal contacts of I I I I key 24| from the power unit of the' monitoring 1 channel: toi the Ihi'ghifrequency :channel 20 I, this 11 high frequencyIchannel isIiin conditioniforrecep-I 1 tion, IIf then reception is received, such recepf I itio'nwill betrans'mitted 1'to the: monitoring chan- 11 rne'l209f and-bef made rmanifesti by a signalingtonel -1 Ioryoice'1 in the lIoud-'speaker12l01' I '1* 1 I 1 1 f 1 yThe:rnsmit'or hearing the tone or 'Voice 'reception' and noting the lighted lamp 26 I, is apprised oi the i .I fa'ct that reception is Abeing received over? the first 1 I `high 'frequency channel 2011.. Hei will thenoper-I 1 j L f atef key 241|` to either; its .upperor lower position' f I Idependentupon the availability of ian: intermedii vate frequency service channel. It will be assumed that service channel No. I is available and that the key is operated to its lower position, thereby opening at its lower left normal contact the previously traced circuit of relay 23|. Relay 23| upon releasing disconnects channel I from the monitoring channel 209. At its inner lower left alternate contact, key 24| establishes the operating circuit of switching relay 2| I which may be traced from bus-bar 2I1 through lter 238, winding of relay 2| I, lter 240, contacts of key 24| to ground. Relay 2II upon operating functions in the same manner as relay 23| to establish the continuity of conductors IF and B between the output of channel 20| and the input of intermediate frequency channel 201 whereby a service connection is established to the No. I service channel. At its lower right contacts key 24| transfers the screen grid and plate potential supply conductors S and P of channel 20| from the power unit of the monitoring channel 209 to the power unit of the intermediate frequency service channel 201. At its outer lower left contact key 24| also establishes a circuit for immediately advancing the selector switch 250 to its next position for monitoring on the second high frequency channel 202. This circuit may be traced from bus-bar 2I1, winding and interrupter contacts of stepping magnet 251, conductor 269, lower left alternate contacts of key 24 I, left normal contacts of key 25|, conductor 21|, terminal and wiper 268 of switch 250 to ground at the back contact of relay 258.

With switch 250 now in position 2 a circuit is established from bus-bar 2I1, lter 238, winding of switching relay 232, lter 241, and in parallel therewith through 1amp1262,left normal contacts I, ofikey 2 42g1leit normal contacts Aof key '1252, conf 1 pastor-212,110.2 terminaland wiper-,soiswitch 1250A to ground; :at the back-1 contact oigrelay 256. I, 1 1 I 1 I 1 Relay 2312; operates andiamp 1262. lights. Relay i232' upon operating functions inthe same manner 1 I I l I n key v22i2IIfrorn the power unit 10i themonitoring zspeaker; |0- whether reception is in; fact I. being. I 1 g received over channel 2021 and wishes to make a; L I I -iongerv test than wouldbe possible; during the interval thatthe selector y2E '0;n;ormally pauses 1in 1 1 1 .afnyI of iits Imonitoring. positions.. The 1 monitor will therefore operate key 252 to its upper position tors 11F and B :between the output ,of channelA 2202 and theinput of the monitoring'channel: 2001a1nd I I to remove blocking .bias-normally; applied from. the power unit of .the lmonitoring channel. over conductor BB and the lower back contact :of relay I 1 1 1 I 23211130 the biasing conductor: B ofchannel 202.I 1 I 1 I 1 I With the blocking biasrernoyed and the screen. 1 igrid and plate potentials supplied over supply o0n-I 1 1 1 ductors .S and P and the right normalcontacts of 1 1 1 channel to the; high. frenuency-,channel 2021, vthis- 1 1 I 1 I high frequency channel conditionedforrecap-z1v I1 tion; l'lhelamp 262 being lightedfthe monitor is u fapprisedofthe fact that-the monitoring: channel is associatedI with the second vhigh ifrequency I1 I channel 202.1 IItwill ne assumed 1|:1hat the monitor is not certain rfrom* the operation foi the loudf i 1 1 1 f .thereby establishinga holding; circuitgioriswitch*1 1 1 g ving relay1232i to; maintain. channel 202; connected I l l. I Iwiththe monitoring -channel:. This circuit may: 1 I 1 1 I 1 be tracedrfrorn bus-bar 21I1gthrough iilter2301, 1winding ofrelay 232,y filter 241,1 eit normal con* tacts` of. key 24.2, upper left alternate contactsoi 1 1 key1252 toI ground! I lliarnp :262. is alsomaintaincd 1 v I l y circuit from ground over :conductor 210. through the winding of relay 258 to the bus-bar 2I1. Relay 258 opens the current supply circuit through the rectifier 229 and relay 231 to stop the further operation of the selector switch and removes ground from wiper 268 to insure against the operation of the switching relay 233 and the lighting of the lamp 263 of the next channel should switch 250 be advanced another step.

The monitor may now wait for a suiiicient time to convince him as toy the presence of reception on channel 202. It will be assumed that he hears no signaling tone or Voice reception from the loudspeaker 2I0 and therefore restores key 252 to its normal position thereby releasing relay 258. The selector switch circuits are now conditioned for operation and in due course switch 250 advances its wiper 268 to the next position. Wiper 268 upon leaving its No. 2 terminal opens the operating circuits of switching relay 232 and lamp 262 and since the holding circuits I'or this relay and lamp have been opened by the restoration of key 252, relay 232 releases to disconnect channel 202 from the monitoring channel 209 and lamp 262 becomes extinguished. When wiper 268 engages its No. 3 terminal a circuit is completed from. bus-bar 2II through lter 238, winding of switching relay 233, iilter 248 and in parallel through lamp 263, left normal contacts of keys 243 and 253, conductor 213, wiper 258 to ground at the back contact of relay 258. Relay 233 now operates to connect channel 203 to the monitoring channel and lamp 263 lights to apprise the monitor that such monitoring connection has been established. In a similar manner the fourth and fifth high frequency channels, not shown, are

shted over a; parallel brancher thiscircuit.; 1 .At I j 1 .its upper vright contacts key I252: establishes .a 1 1 I -1 l I 1 connected with the monitoring channel as the selector switch advances through its fourth and fth positions. It will be assumed that upon the association of each of these channels with the monitoring channel, no reception is indicated by the loud-speaker 2 i il.

When switch 25S reaches its sixth position, a circuit is established from bus-bar 2H through lter 238, winding of switching relay 23e, filter 2&9, and in parallel through lamp 266,1eit normal contacts of keys 225 and 256, conductor 2`i6, wiper 26s to ground at the back contact of relay 258. Relay 23% now operates to connect the No. S channel 2c@ to the monitoring channel and lamp 282 lights. It will now be assumed that a signaling tone or voice reception is produced by the loud-speaker 2 l). The monitor hearing this tone or voice reception and noting that lamp ZEG is lighted is apprised of the fact that the reception is being received on channel 286 and will proceed to connect channel 206 with a free intermediate frequency service channel. If channel 29S is available he will operate key 2li@ to its upper position thereby opening at its upper left normal contacts the previously traced circuit of relay 2%. Relay 23S upon releasing disconnects channel 2536 from the monitoring channel 259.

At its inner upper left alternate contacts, key

2li@ establishes an operating circuit for switching relay 226 which may be traced from bus-bar 2H through filter 228, Winding of relay 228, filter 2i?, contacts of key 246 to ground. Relay 226 upon operating establishes the continuity of conductors IF and B between the output of channel 206 and the input of intermediate frequency channel 29S whereby a service connection is established to the No. 2 service channel. At its upper right contacts, key 245 transfers the screen grid and plate potential supply conductors S and P of channel 285 from the power unit of the monitoring channel 209 to the power unit of the service channel 2&8. At its outer upper left contact, key 246 also establishes a circuit for immediately advancing the sequence switch 25B to its next position. This circuit may be traced from bus-bar 2 il, winding and interrupter contacts of stepping magnet 251 conductor 25S, upper left alternate and lower left normal contacts of key 2136, left normal contacts of key 25E, conductor 276, wiper 268, to ground at the back contact of relay 258.

Since only six of the possible ten high frequency channels have been equipped, as soon as wiper 26S advances to its seventh terminal position it is immediately advanced to its first terminal position, over a circuit extending from bus-bar 2H, winding and interrupter contacts of stepping magnet 257, strapped terminals and wiper 268 of switch 2523, to ground at the back contact of relay 258. With the wiper 258 now positioned on the first terminals of its arc, monitoring on the first high frequency channel now proceeds. If the rst channel is still connected with the No. i service channel and key 2li! is still operated to its lower position, switch 255 will pass by this channel quickly without operating the switching relay 231 as the circuit of this switching relay will be open at the lower left normal contacts of key 2M. The circuit by which the switch 25u is advanced into position 2 may be traced from bus-bar 2H, winding and interrupter contacts of magnet 25'?, conductor 269, lower left alternate contacts of key 2li i, left normal contacts of key 25 i conductor 2li, wiper 26B, to ground at the back contact of relay 258.

The switch 250 then proceeds in the manner previously described to connect the high frequency channels to the monitoring channel in rotation so long as the key 227 is operated.

Should it be desirable to skip monitoring on any channel at any time, the monitor may do so by operating the second key associated with that channel to its lower position. For example, should the key 25! of the first channel 26! be so operated, when the switch 25B reaches its first position in which monitoring on that channel would ordinarily be made, a circuit is established for immediately advancing the switch to its second monitoring position which circuit may be traced from bus-bar 2 l l, Winding and interrupter contacts of stepping magnet 25%', conductor 269, lower left alternate contacts of key 251, conductor 2li, rst position terminal and wiper 288 of switch 25) to ground at the back Contact of relay 25S.

What is claimed is:

l. In a signaling system, a plurality of high frequency receiving channels, a plurality of intermediate frequency channels, certain of which are used for completing service connections and one of which serves as a monitoring channel, switching means for connecting said high frequency channels in rotation to said monitoring channel, and manually operated switching means for connecting any one of said high frequency channels to any one of said intermediate frequency service channels.

2. In a signaling system, a plurality of high frequency receiving channels, a plurality of intermediate frequency channels, certain of which are used for completing service connections and one of which serves as a monitoring channel, a plurality of groups of switching relays, said groups of relays being allotted respectively to said intermediate frequency channels and each comprising as many relays as there are high frequency channels, automatic switching means for operating the relays of one group in rotation to successively connect said high frequency channels to said monitoring channel, and manually operable means for controlling the relays of the other groups to connect any one of said high frequency channels to any one of said intermediate frequency service channels.

3. In a signaling system, a plurality of high frequency receiving channels, a plurality of intermediate frequency channels, certain of which are used for completing service connections and one o-f which serves as a monitoring channel, a plurality f groups of switching relays, said groups of relays being allotted respectively to r said intermediate frequency channels and each comprising as many relays as there are high frequency channels, a signal associated with each high frequency channel, automatic switching means for operating the relays of o-ne group in rotation to successively connect said high frequency channels to said monitoring channel and to successively operate sai-d signals to indicate when each highA frequency channel is associated with said monitoring channel, and manually operatable means for controlling the relays of the other groups to connect any one of said high frequency channels to any one of said intermediate frequency service channels.

Ll. In a signaling system, a plurality of high frequency receiving channels over which different signaling frequencies identifying diiferent transmitting stations may be received, a plurality of intermediate frequency channels, certain of which are used for completing service connections and one of which serves as a monitoring channel, a plurality of responsive devices connected to the output of said monitoring channel, each of said devices being responsive to a different signaling frequency, a plurality of banks of signal lamps, each bank of lamps being allotted to one of said high frequency channels, switching means for successively connecting each of said high frequency channels to the input of said mom'- toring channel and for simultaneously rendering the allotted banks of lamps subject to the control of said responsive devices, and manually operated switching means for connecting any one of said high frequency channels to any one of said intermediate frequency service channels.

5. In a signaling system, a plurality of high frequency channels over which different signaling frequencies identifying different transmitting stations may be received, an intermediate frequency channel, a plurality of transformers associated with the output circuit of said intermediate frequency channel, each tuned to be responsive to a different signaling fr-equency, a detector tube in the output circuit of each of said transformers, a relay associated with the output circuit of each of said tubes and responsive only to the reception of a p-articular signaling frequency, a plurality of indicators allotted respectively to said high frequency channels and each comprising a group of relays and lamps controlled thereby, the relays of each of said indicators being selectively responsive to said first relays, and means for successively associating each of said high frequency channels with the input of said intermediate frequency channel and for simultaneously rendering the `groups of relays of said indicators successively subject to the control of said first relays.

6. In a signaling system, a high frequency channel over which different signaling frequencies identifying different transmitting stations may be received, an intermediate frequency channel associable therewith, a plurality of transformers associated with the output circuit of said intermediate frequency channel, one of said transformers being untuned and the others of said transformers being tuned to be responsive respectively to different signaling frequencies, a detector tube in the output circuit of each of said tuned transformers, a relay associated with the output circuit of each of said tubes, each of said relays being rendered responsive only to the reception of a particular signaling frequency, a tube in the output circuit of said untuned transformer and effective to increase the bias on th-e grids of said detector tubes in response to static disturbances or voice frequency currents, and signal lamps selectively responsive to said relays for indicating the identity of the transmitting stations.

'7. In a signaling system, a plurality of high frequency receiving channels, an intermediate frequency monitoring channel, a switching relay and a key allotted to each of said high frequency channels, a selector switch, operating circuits for said relays successively established during the advance of said switch whereby said relays are controlled to connect said high frequency channels in rotation to said monitoring channel, and means controlled by the key associated with any one of said high frequency channels to open the circuit of the corresponding switching relay and to cause said switch to pass by such channel without effecting its connection to said monitoring channel.

8. In a signaling system, a plurality of high frequency receiving channels, a plurality of intermediate frequency channels, certain of which are used for completing service connections and one of which serves as a monitoring channel, a plurality of groups of switching relays, said groups of relays being allocated respectively to said intermediate frequency channels and each comprising as many relays as there are high frequency channels, automatic switching means for operating the relays of one group in rotation to successively connect said high frequency channels to said monitoring channel, a key individual to each relay of said other groups for controlling said relays to connect any one of said high frequency channels to any one of said service channels, a skip monitoring relay associated with each high frequency channel and operative when said channel is associated with any one of said service channels, each of said latter relays when operated being effective to cause said switching means to pass by the channel with which it is associated without causing the connection thereof to said monitoring channel.

9. In a signaling system, a plurality of high frequency receiving channels, a plurality of intermediate frequency channels, certain of which are used for completing service connections and one of which serves as a monitoring channel, a plurality of groups of switching relays, said groups of relays being allocated respectively to said intermediate frequency channels and each comprising as many relays as there are high frequency channels, automatic switching means for operating the relays of one group in rotation to successively connect said high frequency channels to said monitoring channel, a key individual to each relay of said other groups for controlling said relays to connect any one of said high frequency channels to any one of said service channels, and means controlled by the operation of any one of said keys to cause said switching means to pass by the high frequency channel with which said operated key is associated without causing the connection of said channel with said monitoring channel.

l0. In a signaling system, a plurality of high frequency receiving channels, a` plurality of intermediate frequency channels, certain of which are used for completing service connections and one of which serves as a monitoring channel, a plurality of groups of switching relays, said groups of relays being allocated respectively to said intermediate frequency channels and each comprising as many relays as there are high frequency channels, automatic switching means for operating the relays of one group in rotation to successively connect said high frequency channels to said monitoring channel, and a key individual to each relay for controlling said relays to connect any one of said high frequency channels to any one of said intermediate frequency channels.

ll. In a signaling system, a plurality of high frequency channels, a plurality of intermediate frequency channels, certain of which are used for completing service connections and one of which serves as a monitoring channel, a plurality of groups of switching relays, said groups of relays being allocated respectively to said intermediate frequency channels and each comprising as many relays as there are high frequency channels, automatic switching means for operating the relays of one group in rotation to successively connect said high frequency channels to said monitoring channel, a key individual to each relay of said other groups for controlling said relays to connect any one of said high frequency channels to any one of said service channels, and a key individual to each relay of said one group for controlling said relays to connect any one of said high frequency channels to said monitoring .channel independent of said switching means.

12. In a signaling system, a plurality of ln'gh frequency channels, a plurality of intermediate frequency channels, certain of which are used for completing service connections and one of which serves as a monito-ring channel, a plurality of groups of switching relays, said groups of relays being allocated respectively to said intermediate frequency channels and each comprising as many relays as there are high frequency channels, automatic switching means for operating the relays of one group in rotation to successively connect said high frequency channels to said monitoring channel, a key individual to each relay of said other groups for controling said relays to connect any one of said high frequency channels to any one of said servicey channels, a key individual to each relay of said one group for controlling said relays to connect any one of said high frequency channels to said monitoring channel independent of said switching means, and means controlled by any one of said keys for causing said switching means to pass by the channel with which the operated key is associated.

HAROLD M. PRUDEN. 

